Carburizing box with inner surface resistant to carbon penetration



Aug. 3, 1937. H HARRIS 2,088,594

CARBURIZING BOX WITH INNER SURFACE RESISTANT TO CARBON PENETRATION Filed Oct. 23, 1936 w, 19% MJQLW Patented Aug. 3, 1937 UNITED STATES PATENT OFFICE 2,088,594 CARBURIZING BOX WITH INNER SURFACE RESISTANT TO CARBON PENETRATION The present invention relates to carburizing boxes for use in heat treating furnaces; this application being in part a continuation of my copending application Serial No. 19,196, filed on May Most carburizing boxes have a relatively short life due to the injurious effects of the varying conditions to which they are subjected in use. Specifically, among the difficulties which develop in carburizing boxes are that the boxes are penetrated by carbon, become porous and permit gas leakage therethrough, and solid carbon streaks form in the porosities while the metal is hot,

which create a strain when the metal of the box contracts. Varying combinations of alloys have been developed for use in carburizing boxes to overcome these difliculties, and it has been found that a box of chromium-nickel-ironcomposition is very well adapted to resist carbon penetration and porosity formation, and thereby to have a longer relative life than ordinary steel alloy boxes.

However, these nickel-chromium-iron boxes are comparatively more expensive, and after a while they too must be laid aside due to carbon penetration at the chromium grain boundaries, the chromium having a definite affinity for carbon. It is, therefore, the main object of my invention to provide a chrome-nickel-iron carburizing box which will be highly resistant to carbon penetration and streaking.

It is a further object of my invention to provide' a carburizing box with an interior surface layer which will resist carbon penetration.

A further object of my invention is to provide a method of treating carburizing boxes to render them more resistant to carbon penetration and the formation of porous spots.

A further object of my invention is to provide a method of coating the interior of carburizing boxes with a layer of material which will make the boxes more resistant to the penetration by carbon and less susceptible to the formation of porous centers.

Further objects of my invention will in part be apparent and in part be pointed out hereinbelow in connection with thedescription of an illustrative embodiment of my improved box and I the method of making the same.

My invention is best adapted to a carburizing box of chromium-nickel-iron composition and will be described in connection therewith, although it may be adapted for use and application but several coatings with other types, principally those of which nickel is an important constituent.

In the annexed drawing, Figure 1 is a perspective view showing a conventional carburizing box undergoing the treatment of my invention, the details being exaggerated for illustrative purposes; and

Fig. 2 is an enlarged similarly exaggerated sectional view through one wall thereon on the line 2-2. my

I spray the inner surfaces of the carburizing box ID with a layer of nickel l2, preferably by means of the Shoup gun l4, whereby the coating material is sprayed as it is melted. Carburizing boxes, in use, are emptied of their contents while still extremely hot. These boxes thus have a deflnite oxidizing atmosphere when exposed to the air at high temperatures. This nickel is thus converted into the simple and higher oxides of nickel in the exposure to high temperatures incidental to use of the box, and functions thereby to resist and reduce any penetration by carbon. This added resistance to carbon penetration is of two kinds: chemical and mechanical; chemical in so far as nickel and its oxides are highly resistant to carbon, and mechanical since a definite thickness of nickel and its oxides is between the box wall and the carbon within the box among the materials being heat-treated.

A single spray coating is ordinarily sufficient, or layers may be sprayed thereon if desired, and the ratio of nickel to other metals in the box correspondinglyincreased.

Having described my invention, what I claim and desire to secure by Letters Patent is:

1. A carburizing box of alloy material comprising nickel, chromium, iron, etc., and an interior surface layer of oxides of nickel, said oxides being present due to a deposited interior surface layer of nickel, whereby the chemical and mechanical resistance to carbon penetration is increased.

2. The process of imparting enhanced chemical and physical resistance to carbon penetration to a carburizing box of an alloy material comprising nickel, chromium, iron, etc., which consists of spraying the interior surface of the box with nickel in molten, finely-divided state, thereby depositing a layer of nickel thereon, and thereafter exposing the box to high heat converting said nickel layer into a layer of oxides of nickel.

HENRY HARRIS. 

